A FLAME RETARDANT POLYAMIDE RESIN COMPOSITION

Abstract: A flame retardant polyamide resin composition made from 100 weight parts of a polyamide resin, 10 to 100 weight parts of a brominated polystyrene, and 1 to 20 weight parts of magnesium hydroxide or magnesium oxide, or made from 100 weight parts of a polyamide resin, 10 to 100 weight parts of a brominated polystyrene, 0.5 to 10 weight parts of magnesium hydroxide or magnesium oxide, and 0.5 to 10 weight parts of antimony oxide.

Description: TITLE A FLAME RETARD ANT POLYAMIDE RESIN COMPOSITION BACKGROUND OF THE INVENTION The present invention concerns a flame retardant polyamide resin composition that yields moldings which are characterized by excellent high-temperature stability and mechanical characteristics and which are impervious to corrosion even when used for a long time. Polyamide resins are characterized by excellent mechanical characteristics, moldability, and chemical resistance and have therefore been used in automotive parts, electric/ electronic components, mechanical components, and many other applications. In particular, the need for flame retardancy is strong in the case of electric and electronic components, so the resins must satisf Class V-O requirements of the UL standard. This is the reason that flame retardant polyamide resins obtained, for example, by compounding brominated polystyrenes and antimony oxide into polyamide resins are now widely known. The shortcomings of resin compositions obtained by the compounding of brominated polystyrenes and antimony oxide are that when the components are kneaded in high-temperature conditions or when the shear rate is high during the kneading of the components, the resin compositions undergo decomposition, their processing during manufacturing and molding is markedly impaired, and the mechanical characteristics of moldings are adversely affected. To overcome these shortcomings, stability at high temperatures is improved by compounding sodium antimonate instead of antimony oxide, but sodium antimonate must be compounded in a larger amount than antimony oxide in order to obtain a fire retardancy comparable to that of a polyamide resin composition containing compounded antimony oxide. The mechanical characteristics of resin compositions, however, tend to be impaired when a large amount of sodium antimonate is compounded with the aforementioned polyamide resin composition. Another disadvantage is that an increase in process temperature additionally impairs the thermal stability of the resin composition when the brominated polystyrene contained in the resin composition obtained by the compounding of sodium antimonate and the brominated polystyrene has a high viscosity, that is, when, for example, the viscosity is at least 700 pascals at a temperature of 250 °C and a shear rate of 100 sec -1 . In addition, sodium is eluted and corrosion develops when moldings are used for a long time. The objective of the present invention is to offer a flame retardant polyamide resin composition capable of offering moldings which are highly stable at high temperatures, do not decompose during kneading and molding, possess excellent mechanical characteristics, and are unlikely to undergo corrosion even when used for a long time. The present invention, which allows the stated objective to be attained, concerns a flame retardant polyamide resin composition which is characterized by essentially comprising 100 weight parts of a polyamide resin, 10 to 100 weight parts of a brominated polystyrene, and 1 to 20 weight parts of magnesium hydroxide or magnesium oxide. The polyamide resin used in the present invention is one which is obtained by random ring-opening polymerization, aminocarboxylic acid polycondensation, diamine and dicarboxylic acid polycondensation, or diamine and aromatic carboxylic acid polycondensation. Specific examples include polyamides 6, 12, 11, 6-6, 6-10, and 6-12. An aromatic polyamide with a melting point of 280 to 340°C is preferred. It is particularly suitable to use an aromatic polyamide resin which comprises aromatic carboxylic acid component units that consist of terephthalic acid or a mixture of terephthalic acid and isophthalic acid containing no more than 40 mol% of isophthalic acid, and aliphatic diamine component units that consist of a mixture of hexamethylenediamine and 2- methylpentamethylenediamine containing 40 to 90 mol% of hexamethylenediamine. Stability at high temperatures is markedly improved by the use of an aromatic polyamide with a melting point of 280 to 340 °C. Such an aromatic poly amide resin can be manufactured by a known polycondensation technique. Polyamide 6-6 may be blended into the aromatic polyamide resin; terephthalic acid, a mixture of terephthalic acid and isophthalic acid, adipic acid, hexamethylenediamine, and 2-methylpentamethylenediamine may also be subjected to polycondensation together with the resin. Examples of the brominated polystyrenes of the present invention include poly(dibromostyrene), poly(tribromostyrene), and poly(pentabromostyrene). The content ranges from 10 to 100 weight parts with respect to the polyamide resin. When the content is lower than 10 weight parts, it is impossible to attain Class V-O fire retardancy, and when the content exceeds 100 weight parts, the mechanical strength becomes inadequate. The content of the magnesium hydroxide or magnesium oxide used in the present invention should be 1 to 20 weight parts, and preferably 2 to 8 weight parts. A content that is lower than 1 weight part produces no fire retardancy effect. When the content exceeds 20 weight parts, the mechanical strength and tensile elongation decrease, and the polyamide resin decomposes when a large amount is compounded. Magnesium hydroxide and magnesium oxide may be used individually or as a combination. A flame retardant polyamide resin composition with an even better processibility is obtained when antimony oxide is compounded in addition to magnesium hydroxide or magnesium oxide. The contents of components in this case should be 10 to 100 weight parts for the brominated polystyrene, 0.5 to 10 weight parts for magnesium hydroxide or magnesium oxide, and 0.5 to 10 weight parts for antimony oxide, per 100 weight parts of the polyamide resin. When the content of antimony oxide is lower than 0.5 weight parts, no flame retardancy effect is produced, and when the content exceeds 10 weight parts, the mechanical strength and tensile elongation decrease. Glass fiber, carbonized fiber, potassium titanate, whiskers, talc, mica, and other inorganic fibers may also be compounded with the polyamide resin composition of the present invention. Thermal stabilizers, plasticizers, antioxidants, nucleators, dyes, pigments, mold-release agents, and other additives can also be compounded in addition to the aforementioned components with the proposed polyamide resin composition as long as its characteristics are not adversely affected. The undesirable toxicity induced by antimony can be reduced or completely eliminated by the substitution of some or all antimony oxide with the magnesium hydroxide or magnesium oxide compounded into the polyamide resin composition of the present invention. In addition, the resin composition does not decompose, nor does processibility deteriorate markedly during manufacturing and molding, even when the components are kneaded or molded in high-temperature conditions or when a high shear rate is developed during the kneading of the components. This makes it possible to offer a resin composition with satisfactory thermal stability, even when a highly viscous brominated polystyrene is used. Another advantage is that because no sodium antimonate is used, there is no undesirable sodium-induced corrosion, and the mechanical characteristics are improved in comparison with the Class V-O characteristics obtained using sodium antimonate. EXAMPLES The present invention will now be described in detail through practical examples. Practical Examples 1 Through 9; Comparative Examples 1 and 2 Components were premixed for 20 minutes in a tumbler and then made into resin pellets by being melted and kneaded at a temperature of 320 °C and a screw speed of 200 rpm using a TEM 35B biaxial extruder manufactured by Toshiba Machine; thermogravimetric analyses (TGA) were performed using the resulting resin pellets. Standard test pieces were fabricated, and mechanical characteristics were measured based on the following test methods. Tensile Strength: ASTM D 638-58T Elongation: ASTM D 638-58T Flex Modulus: ASTM D 790-58T Flexural Strength: ASTM D 790-58T Notched Izod: ASTM D 256-56 For combustion testing, UL-94 combustion test pieces with a thickness of 1/32 inch were molded, and tests were conducted in accordance with UL standards. The components shown in Table I were as follows: Polyamide Resin: Aromatic polyamide resin comprising terephthalic acid and a mixture of hexamethylenediamine and 2- methylpentamethylene-diamine; the diamine component contained 50 mol% hexame¬ thylenediamine and 50 mol % 2-methylpentamethylenediamine Poly(dibromostyrene): PDBS 80 manufactured by Great Lakes; viscosity 300 pascals at a temperature of 250"C and a shear rate of 100 sec" 1 ("Capillograph IB"; Toyo Seiki) Poly(tribromostyrene): "Pyro-Chek 68PB"; manufactured by Nissan Ferro. Viscosity at least 1000 pascals at a temperature of 250 C and a shear rate of 100 sec -1 ("Capillograph IB"; Toyo Seiki) Magnesium Oxide: "Micro-Mag 3-150"; manufactured by Kyowa Kagaku Magnesium Hydroxide: "Kisuma 5EU"; manufactured by Kyowa Kagaku Antimony Pentoxide: "San-Epok NA 1030"; manufactured by Nissan Chemical Sodium Antimonate: "San-Epok NA 1070L"; manufactured by Nissan Chemical In comparison with any of the compositions of the comparative examples, the compositions of the practical examples possessed improved thermal stability and mechanical characteristics. A comparison between the compositions of Practical Examples 1 to 3 and the composition of Practical Examples 6 to 9 shows that excellent thermal stability can be obtained even with the use of highly viscous brominated polystyrenes. Table I Practical Comparative Examples Examples 1 2 3 4 5 6 7 8 9 1 2 Polyamide Resin (wt%) 41 41 41 41.3 41 43 43 43 43 40.8 40.8 Glass Fiber (wt%) 35 35 35 35 35 35 35 35 35 35 35 Poly(dibromostyrene) (wt%) 20.00 20.00 20.00 19.00 19.00 — — — — 18.00 — Poly(tribromostyrene) (wt%) — — — — — 18.00 18.00 18.00 18.00 — 18.00 tn C Sodium Antimonate (wt%) — — ... — — — — — — 6.20 5.20 DO I H Antimony Pentoxide (wt%) — 2.00 2.00 4.00 4.00 — — 2.00 2.00 — — H C Magnesium Oxide (wt%) — 2.00 — 0.70 — 4.00 — 2.00 — — — H m IΛ Magnesium Hydroxide (wt%) 4.00 — 2.00 — 1.00 — 4.00 — 2.00 — — _C m m Thermogravimetric Analysis 1.244 1.201 1.126 0.80 0.95 0.387 0.6998 0.47 0.70 2.716 16.94 H (%) 13 c Tensile Strength (kgf/cm^) 1891.10 1724.80 1715.10 792.6 1753.6 1981.80 2105.90 1797.00 1732.90 1456.30 1269.00 r- rn K> Elongation (%) 1.60 1.50 1.36 1.65 1.68 1.67 1.87 1.40 1.45 1.23 1.19 cn Flexural Strength (kgf/cm^) 2740.30 2502.40 2482.20 470.00 2468.6 2859.90 3001.40 2615.00 2650.00 2124.10 1947.00 Notched Izod (kgf-cm/cm) 11.30 8.20 7.90 8.70 9.60 8.20 9.60 6.40 5.90 6.90 5.70 Fire Retardancy (1/32") V-O V-O V-O V-O V-O V-O V-O V-O V-O V-O V-O It can thus be seen that the polyamide resin composition of the present invention is a resin composition which possesses excellent high- temperature stability, does not decompose during kneading and molding, and exhibits superb mechanical characteristics even when a highly viscous brominated polystyrene is used. In addition, the antimony- induced toxicity is reduced, and moldings obtained using the proposed polyamide resin composition are unlikely to undergo corrosion when used for a long time.

Claims: CLAIMS 1. A flame retardant polyamide resin composition which is characterized by comprising 100 weight parts of a polyamide resin, 10 to 100 weight parts of a brominated polystyrene, and 1 to 20 weight parts of magnesium hydroxide or magnesium oxide. 2. A flame retardant polyamide resin composition which is characterized by comprising 100 weight parts of a polyamide resin, 10 to 100 weight parts of a brominated polystyrene, 0.5 to 10 weight parts of magnesium hydroxide or magnesium oxide, and 0.5 to 10 weight parts of antimony oxide. 3. The flame retardant polyamide resin composition according to Claim 1 or 2 wherein the polyamide resin is an aromatic polyamide resin with a melting point of 280 to 340 °C. 4. The polyamide resin composition according to Claim 3 wherein the aromatic polyamide resin with a melting point of 280 to 340 °C comprises aromatic carboxylic acid component units that consist of terephthalic acid or a mixture of terephthalic acid and isophthalic acid containing no more than 40 mol% of isophthalic acid, and aliphatic diamine component units that consist of a mixture of hexamethylenediamine and 2-methylpentamethylenediamine containing 40 to 90 mol % of hexamethylenediamine. 5. The polyamide resin composition according to Claim 3 wherein the aromatic polyamide resin with a melting point of 280 to 340 °C is a polyamide resin that comprises (a) repeating units composed of aromatic carboxylic acid component units that consist of terephthalic acid or a mixture of terephthalic acid and isophthalic acid containing no more than 40 mol% of isophthalic acid, and aliphatic diamine component units that consist of a mixture of hexamethylenediamine and 2- methylpentamethylenediamine containing 40 to 90 mol% of hexamethylenediamine, and (b) repeating units composed of adipic acid component units and hexamethylenediamine component units.

Inventors: HAYASHI RYUICHI, HAYASHI, RYUICHI
Applicants: DU PONT, HAYASHI RYUICHI, E.I. DU PONT DE NEMOURS AND COMPANY, HAYASHI, RYUICHI
Application year: 1994
Main classification: C08K5
IPC codes: C08K3, C08K7, C08L25, C08L73, C08L77, C09K21